The present invention relates to position sensor emulators for wound rotor motors and generators of aerospace and industrial power and drive systems. Further, the invention relates to sensorless control of wound rotor motors and generators.
Conventionally motor controllers for applications requiring a controlled torque use discrete sensors to determine rotor position in a rotating machine. This technique however increases system complexity and decreases system reliability. The electric machine must have a sensor built in or attached mechanically to the rotor. Interfaces and wiring must be added for control (excitation) and feedback signals between the controller and the sensor. Typical sensors include resolvers, encoders, and the like. The location of the rotating machine could be far from the controller, creating the need for unwanted extra wiring in the system.
A conventional motor control system having a position sensor is shown in FIG. 1A. The primary components of the system include a power source 110, a controller 120, a motor/generator 130 and a speed/position sensor 140. The Motor/Generator and Starter/Generator terms are used interchangeably in the following descriptions and claims. The controller 120 includes an inverter controls 126 that receives signals from the sensor 140 (e.g., speed/rotor position) and the motor/generator (e.g., current, voltage). These signals are used to control the main inverter 122 and exciter inverter 124, thereby providing a conventional closed loop system to regulate the current as a function of the speed of the motor/generator 130, as will be appreciated by those skilled in the art.
FIG. 1B illustrates a block diagram of a sensorless system. As is apparent from the block diagram, the sensor and related signals to the controller 120 are absent. Those skilled in the art will appreciate that this requires the controller 120 to process the rotor position/speed of the motor/generator to allow closed loop current regulation or to execute certain control functions (e.g., current control) or operate in an open loop mode.
However, sensorless motor control techniques can increase system reliability and eliminate the need for extra wiring in the system. In addition these techniques will eliminate the need for a position sensor and also reduce the system cost. A sensorless motor control technique is a more flexible/adaptable solution for a motor drive system than one that relies on a separate position sensor. It is particularly valuable for aircraft system where increased reliability and reduction of weight (e.g., through elimination of the sensor and additional wiring) are extremely important.
Motor controller applications in systems with existing electrical machines can use a sensorless motor control scheme. For example, sensorless control systems are advantageous in retrofit applications, where a sensor and appropriate wiring may be unavailable and not easily installed. Some of these systems have synchronous generators that can be used as a motor/generator but they do not have discrete sensors. Additional applications for this technique include motor controllers in the environmental control systems, electric power systems, industrial drive systems, and the like.
U.S. Pat. No. 5,920,162 issued to Hanson et al. describes a system that utilizes feed through from the exciter winding of twice the fundamental frequency of excitation thereof which is detected synchronously in one of a plurality of stator phase windings of a main motor generator. The one of a plurality of stator phase windings is maintained in a non-commutated state during operation as a motor to determine rotor position of the main motor generator for control of commutation of current in all other commutated stator phase windings. The amplitude modulation of the voltage across each stator phase winding which is maintained in a non-commutated state represents the rotary position of the rotor of the main motor generator which is used to control commutation of current flow in an at least one and preferably all remaining commutated stator phase.
However, although the above-described system operates as in a sensorless mode, it requires that the position sensing take place only on the non-commutated stator windings. Accordingly, the position sensor emulation must shift from phase to phase as respective phases are commutated, which complicates the sensor emulation. Therefore, it is desired to have a sensor emulation technique and sensorless control system that truly emulates a continuous position sensor and is not dependent on the commutated state of the stator windings. Further, the prior art sensorless systems fail to provide an initial position sensing, which is beneficial at start-up under high load torque of the motor/generator.
In accordance with the present invention, the deficiencies in prior systems are overcome by providing a position sensor emulator that processes continuously the rotor position from, and including, the standstill to a certain speed. This position sensor emulator includes a first bandpass filter that filters phase voltage signals from a stator of a synchronous machine. A converter that converts the filtered phase voltages into balanced two-phase quadrature signals. Additionally, the position sensor emulator can provide a rectifier that rectifies exciter voltage signals of the synchronous machine and a second bandpass filter that filters the rectified exciter voltage signals to generate a reference signal.
According to another embodiment of the invention, a method for emulating a position sensor comprises: bandpass filtering phase voltage signals from a stator of a synchronous machine; and converting the filtered phase voltages into balanced two-phase quadrature signals. Additionally, the method can provide a reference signal by rectifying exciter voltage signals of the synchronous machine; and bandpass filtering the rectified exciter voltage signals to generate a reference signal.